Wanting to rebuild my 351m out of a 78 f100. What should I do for a performance upgrade? Making it a 400 worth it and if so how to do it? Already has edelbrok carb and intake with dual exhaust and headers.

So I got the engine build which is now a 400m. I cannot get the 78 f100 to idle properly. The fuel pressure is good, there is a new carb on it (edelbrock 600). It will idle high as then it will want to die. When I get it idling not too bad it pretty much stalls when I put it in gear and it misfires. Seems to smooth out when RPMs are up as it has lots of power it's just the idle. It also doesn't want to idle at all on factory timing setting, I have the timing as high as possible without pinging so that it will run. Any ideas?